Proper service of such notice shall be by personal service, residence service, or by registered mail; provided, however, that such notice shall be deemed to be properly served, if a copy thereof is sent by registered mail to the last known address. If any of the parties cannot be located, nor can his address be ascertained, this notice shall be deemed to be properly served if a copy thereof is placed in a conspicuous place in or about the building or structure affected by this notice. If such notice is by registered mail, the thirty day period within which such owner is required to comply with the order or the Building Inspector shall begin as of the date he received such notice. (Ord. 291. Passed 2-28-77.)